The search for systems and methods that provide efficient protection to linear compressor is constant, so that a few known methods and systems make use of sensors for controlling piston displacement, vibration sensors, or still electric devices that measure, for example, voltage and current values applied to the compressor.
It is advisable that the protection methods make use of the smallest amount of additional component possible, so that a method based on physical parameters of the compressor will become advantageous chiefly in financial terms.
The prior art discloses means for controlling linear compressor, for instance, the international publication WO 00/16482 is based on crossing the voltage by zero for the consequent adjustment of the compressor's operation frequency to as close as possible to its resonance frequency.
Further, document U.S. Pat. No. 6,812,597, in spite of measuring the compressor cycle times, treats such times independently, without using a relative signal, as proposed in the present invention. The analysis of the cycle times in an independent manner is more subject to variations between compressors, entailing a not so reliable control.
Additionally, patent U.S. Pat. No. 6,616,414 uses electric signals and parameters of the motor of the linear compressor to control the piston stroke. Such parameters comprise electric current, voltage applied, resistance, inductance, among other.
Although the above-mentioned methods and systems have advantages in a few aspects, none of them is based on the calculation of the difference between the operation semicycles (advance and recoil) of the compressor. Further, they operate as methods for actuating the compressor, not for diagnosis and protection.
By calculating such difference, one reduces the variations that may take place between different compressors, thus making it possible to apply it to resonant linear compressors that use any cooling gas.
The present invention aims the protection of a method and a system applied to a resonant linear compressor, which propose to detect compressor break, the impact of the piston against the valves plate and undesired resonances of the mechanism, among other aspects.
The method and the system proposed take are based on the measurement of the advance and recoil times of the compressor piston. Preferably, such times are determined from the piston position and, more specifically, from the crossing by zero of the counter electromotive force (CEMF/FCEM) of the electric motor of the linear compressor.
Subtracting the recoil (suction) time from the advance (compression) time, one obtains a determining decision parameter to achieve the objectives of the present invention.
From the determination of this decision parameter, one can detect the incorrect operation of the compressor and prevent future failures, thus operating as a decision and diagnosis parameter of the linear compressor.